Canon LBP1760P, Service Manual

Page: 70 / 394

1. Electrostatic latent image formation block
This block follows two steps to produce an electrostatic latent image on the photosensitive drum.
When Step 2 of this block is completed, negative charge remains in the unexposed “dark” areas;
however, those in the exposed “light” areas are eliminated.
This image of negative charges on the drum is invisible to the human eye, so it is called an
“electrostatic latent image.”
Figure 2-4-5
Step 1: Primary charging
Figure 2-4-6
In preparation for the latent image formation, a uniform negative potential is applied to the pho-
tosensitive drum surface. For primary charging, the printer uses the charging method, which
directly charges the drum.
The primary charging roller is made of conductive rubber. In addition to DC bias, AC bias is
also applied to the primary charging roller to keep the potential on the drum surface uniform.
The DC bias changes with the developing DC bias.
2 - 32
CHAPTER 2
0
-100
-500
Time t
Exposed area
Unexposed
area
Laser beam exposure
(step 2)
Transfer
(step 4)
Primary
charging
(step 1)
Primary
charging
(step 1)
Surface potential (V)
Photosensitive drum
Primary charging roller
AC bias
DC bias